The present invention relates to methods and apparatus for measuring and predicting parameters of capillary-porous chemically active materials while and after curing. More particularly, the present invention relates to methods and apparatus for non-destructive control and prediction of concrete strength.
As used herein throughout the specification and in the claims section below the phrase xe2x80x9ccapillary-porous chemically active material(s)xe2x80x9d includes cementitious substances, such as, but not limited to, cement, concrete, lime, gypsum, clay and the like.
Concrete, which is used for construction, must be analyzed to determine the structural properties parameters, particularly strength and other physical-mechanical properties of the final cured product, such as its potential for shrinkage.
Concrete is mainly a mixture of water, cement, sand, and gravel. It is known that the fraction of water at all stages of its preparation (e.g., mixing, compaction, curing and hardening), is one of the most crucial parameters, responsible for the strength of the final cured cement stone and concrete.
The water content in concrete appears in two main states (stages) during curing: chemically bound water and physically bound water. The relative water content in formed structure during curing permanently decreases, as a portion of the physically bound water interacts chemically with other concrete components and transforms into a solid phase, whereas another portion is evaporating away from the surface.
It is known that the amount of water that is physically bound has an important influence on the compressive strength and other physical-mechanical properties of concrete at all stages of its formation and utilization.
The traditional prior art methods for testing the strength of concrete require 28 days to complete. The builder usually does not or cannot delay construction 28 days to receive the test results. Rather, the construction usually continues in the hope that the concrete is sound. If in the final analysis, the concrete does not meet the standards, the building may have to be reinforced or even torn down, perhaps incurring major additional costs.
Thus, a method of quick analysis of concrete properties which predicts its final strength or measures the structure strength in situ while hardening, is very desirable.
In addition, when concrete is utilized as a strength bearing member, it would be useful to know when xe2x80x9cshrinkagexe2x80x9d of the concrete has been completed so as not to load the member prematurely, as the premature addition of load to bearing members could lead to cracking of the concrete structure. Shrinkage of cement stone and concrete is correlated to their moisture content. However, to a larger extent, the shrinkage value of cement stone and concrete depends on the size of pores and capillaries in the formed structure, in other words, on the energy level of physically-bound water, interacting with the solid phase.
There is a known method for determination of cement stone and concrete strength according to its porosity. To this effect, see, Roy D. M., Gouda G. R. Porosityxe2x80x94strength relation in porous materials with very high strengthxe2x80x9d J. Amer. Ceramic Soc., 53, No. 10, 1973, pp. 549-550. According to this method, the strength, R, is determined by:                     R        =                              -                          1              k                                ⁢          ln          ⁢                      π                          π              0                                                          (        1        )            
where Π is the general porosity of the cement stone (concrete); Π0 is the porosity at zero strength (R=0), which is approximately 60%; and k is a constant which equals 0.385xc3x97105 MPa.
There is an additional known method for determining cement stone and concrete strength, which is described by Powers T. C. xe2x80x9cThe physical structure and engineering properties of concretexe2x80x9d Port. Cem. Ass. Dept. Bul. 90, Chicago, July 1958.
According to this method, the volume of pores of the cement gel Vg, and the general volume of capillary space Vk of the concrete are experimentally measured; whereas the strength is determined according to the following equation:                     R        =                              A            ⁡                          (                                                V                  g                                                                      V                    g                                    +                                      V                    k                                                              )                                n                                    (        2        )            
where A and n are constants.
The change of the porosity parameters Vg and Vk of Equation 2 during process of hardening is well-supported by data from the literature. To this effect, see, for example, Sheikin A. E. xe2x80x9cStructure durability and crack resistance of cement stonexe2x80x9d. Moscow, Stroyizdat, 1974, p. 191.
Table 1 below, for example, provides porosity related data for a cement stone having a water/cement (W/C) ratio of 0.7 during hardening.
The difficulty and labor input associated with measuring the porosity of concrete and other capillary-porous chemically active materials (especially during hardening) are the shortcomings of the above mentioned methods.
This is due to the necessity to prepare a large quantity of twin-samples, each of which is tested at a particular stage of hardening.
Independent of the applied method for measuring porosity (e.g., nitric porometry, mercury porometry of low and high pressure, etc.), the tested sample should be completely dehydrated. This considerably complicates the testing method, increases its duration and considerably affects the properties of the tested material.
Since cement stone, concrete and other similar materials at any stage of hardening are poly-dispersed moist capillary-porous bodies, it is possible to avoid most of the above-mentioned shortcomings if concrete strength will be determined not by measuring its porosity, but rather by measuring the energy of physically bound water, which is contained in the pores and capillaries of its structure, which is indicative of its porosity and therefore of, for example, its strength.
Water (both in a liquid and gaseous form) is always in a state of thermodynamic equilibrium with the porous solid phase with which it interacts. Thus, the properties of water (viscosity, bounding energy, relaxation time, etc.) are changing in strict accordance with structure formation and, consequently, with the strength growth of the hardening material. To this effect, see, for example, Shtakelberg D. I. xe2x80x9cThermodynamics of water-silicate disperse materials structure-formationxe2x80x9d. Riga, Zinatne, 1984, p.200; and Shtakelberg D. I., Sytchov M. M. xe2x80x9cSelf-organization in disperse systemsxe2x80x9d. Riga, Zinatne, 1990, p175; and Neville M. xe2x80x9cProperties of concretexe2x80x9d Longman Scientific and Technical. NT., 1988, p779.
In a newly compressed cement paste, whose strength is minimal, e.g., in the order of 10xe2x88x921 Mpa, practically all the water is distributed between the grains of a non-hydrated cement. The average distance between the grains is approximately 5-10 xcexcm. At this state, the bond energy of water molecules and the material constitutes only a few kDz/mol.
While hardening, a portion of the water becomes chemically bound, i.e., transforms into a solid state with bond energy in the order of 1000 kDz/mol. Another portion of the water is contained in the pores of the formed cement gel. The size of these pores is less than 10xe2x88x923 xcexcm in diameter and the bond energy in this case is up to 50 kDz/mol. Another portion of the water occupies capillaries of a larger diameter (10xe2x88x922-10xe2x88x921 xcexcm) with bond energy of up to 10-20 kDz/mol.
T2 relaxation time of physically-bound water, contained in capillary-porous structure of chemically-active material changes in a very wide range: from 30-40 xcexcsec (liquid of thin surface layers) up to 3xc3x97106 xcexcsec (bulk water).
During subsequent stages of concrete structure hardening and until its final formation, the water distribution reaches a steady state in which 45-50% of the water is chemically bound, 40% of the water occupies the smaller pores of the cement gel, whereas 10-15% of the water occupies larger capillaries of the concrete structure.
Thus, information pertaining to the energy level of water contained in a concrete structure reflects its porosity, which, in turn reflects its strength. Therefore, it is possible to obtain a far more reliable correlation between the energy of water contained in a concrete structure and its strength.
It was already noted above that physically-chemically bound water in capillary-porous bodies always coexists in thermodynamic equilibrium with the solid phase. Nevertheless, all quality changes developing in cement stone and concrete during the process of structure forming and hardening, such as, chemical dispergation, colloidation, coagulation, crystallization, nucleation, development of inner cracks, etc., are almost immediately reflected by the energy of the liquid stage thereof. This is why, namely, the physically bound water is the most informative component of capillary-porous structures for quality evaluation of energetic level and consequently strength and other physical-mechanical properties.
There are various methods for quantitating (in terms of mass) and qualitating (in terms of energy) chemically and physically bound water in capillary-porous bodies. However, these adsorption methods, some of which are described in the references recited hereinabove, are rather complicated and labor-consuming. Moreover, performance of such measurements in areas of a high relative water vapor pressure (xcfx86=pi/ps) is complicated due to development of capillary condensation. In addition, adsorption methods are suitable solely for testing the samples of cement stone, concrete, etc., with a completely-formed or artificially stabilized structure.
Another method for studying the water content of concrete is neutron hydrometry (see, for example, The Troxler 4430 water/cement gauge). However, neutron hydrometry allows the sole obtainment of quantitative data (mass), whereas no qualitative data (energy) is collectable.
Methods for determining concrete strength and other physical-mechanical properties of concrete samples in situ using nuclear magnetic resonance (NMR) have been developed by the inventors.
NMR methods and apparatuses are well-known for over 50 years and have found an extensive usage in various fields including, but not limited to, oil fields (from oil exploration up to quality determination of petroleum products), food production, medicine, etc. Also, there are numerous and successful applications of NMR-technology in construction and in manufacturing of building materials, particularly for determination of cement qualities.
In order to understand the basics of these methods, a short description of NMR principles is now presented.
The NMR techniques involve placing a sample in a homogeneous magnetic field which is subjected to a pulse of radio-frequency radiation. There are charged particles in the sample which undergo a Larmor precession, i.e., a common rotation superposed by the magnetic field upon the motion of the system of charged particles, all the charged particles having the same ratio of charge to mass.
The absorption of energy by the sample is almost instantaneous. However, the loss of energy, i.e., the nuclear relaxation, is a type of exponential decay process which has time constants. Relaxation occurs when stimulated by local magnetic fields having components at the Larmor frequency, i.e., the angular frequency of the Larmor precession. (The precession and frequency are named after Sir Joseph Larmor, British physicist, who died in 1942.)
There are two distinct types of nuclear relaxation: spin-lattice relaxation and spin-spin relaxation.
Spin-lattice relaxation is an energy effect, and is the loss of the excess energy resulting from the excitation pulse to the surroundings, or lattice, as thermal energy. The time constant associated with spin-lattice relaxation is called T1.
Spin-spin relaxation is an entropy effect, and is related to the loss of stage coherence induced by the excitation pulse. The time constant associated with spin-spin relaxation is called T2.
There are various imaging methods which make use of either the spin-lattice or spin-spin relaxation. One is the constant-time imaging (CTI) method, a variation of which is the single-point imaging (SPI) method. Another method is called the spin-echo method, in which the radio-frequency field is applied in a sequence of two kinds of pulses, separated by a time interval te, and a decayed sequence of echoes are observed after each pulse.
U.S. Pat. No. 4,769,601 describes a method and apparatus for determining the extent of setting of cement and its strength as it sets by means of a pulsed NMR spectrometer. T1 measurements are made while agitating the cement to simulate transportation and placement thereof.
There are articles in the scientific literature describing the use of NMR to study chemical dynamics of cement hydration. M. Bogdan et al., xe2x80x9cSingle-Point Imaging of Partially Dried, Hydrated White Portland Cementxe2x80x9d, J. of Magnetic Resonance, Series A, 116:266-269 discuss using the SPI method. The article states that xe2x80x9cseveral groups have attempted to image water invasion of cured concrete samples using spin-echo imaging methodsxe2x80x9d. These attempts are reported by J. Link et al., Magn. Reson. Imaging, 12:203, and F. Papavassillou et al., J. Am. Ceram. Soc., 76:2109. In regard to these attempts, Bogdan et al. state that xe2x80x9cthe spin-spin relaxation times of water in these dehydration experiments is only a few milliseconds, so the quality of traditional spin-echo images is disappointingxe2x80x9d. Bogdan et al. also state that in their study, xe2x80x9cshort echo-time, one-dimensional, spin-echo profiles of moist cured white-cement paste cylinders displayed poor signal-to-noise and geometric distortions from the ideal profile geometryxe2x80x9d.
Other scientific articles describing the use of NMR to study chemical dynamics of cement hydration, and which all do not use spin-echo methods or fail to successfully use spin-echo methods, include E. Laganas et al., xe2x80x9cAnalysis of Complex H-1 NMR Relaxation Measurements in Developing Porous Structuresxe2x80x94A Study in Hydrating Cementxe2x80x9d, J. Applied Physics, 77:3343-3348; H. C. Gran, xe2x80x9cFluorescent Liquid Replacement Technique, A Means of Crack Detection and /Binder Ratio Determination in High-Strength Concretesxe2x80x9d, Cement and Concrete Res., 25:1063-1074; J. Kaufmann et al., xe2x80x9cOne-Dimensional Water Transport in Concretexe2x80x9d, Materials and Structures, 28:115-124; S. Kwan et al., xe2x80x9cSi-29 and Al-27 MASNMR Study of Stratlingitexe2x80x9d, J. Amer. Ceram. Soc., 78:1921-1926; R. A. Hanna et al., xe2x80x9cSolid State Si-29 and Al-27 NMR and FTIR Study of Cement Pastes Containing Industrial Wastes and Organicsxe2x80x9d, Cement and Concrete Res., 25:1435-1444; X. D. Cong et al., xe2x80x9cEffects of the Temperature and Relative Humidity on the Structure of C-S-H Gelxe2x80x9d, Cement and Concrete Res., 25:1237-1245; S. U. Aldulaijan et al., xe2x80x9cSi-29 MASNMR Study of Hydrated Cement Paste and Mortar Made With and Without Silica Fumexe2x80x9d, J. Amer. Ceram. Soc., 78:342-346; A. R. Brough et al., xe2x80x9cA Study of the Pozzolanic Reaction by Solid State Si-29 NMR Using Selective Isotopic Enrichmentxe2x80x9d, J. Materials Sci., 30:1671-1678; Y. Okada et al., xe2x80x9cInfluence of Starting Materials on the Formation of 1.1-NM-Tobermoritexe2x80x9d, J. Ceram. Soc. of Japan, 102:1148-1153; L. J. Schreiner et al., xe2x80x9cNMR Line Shape-Spin-Lattice Relaxation Correlation Study of Portland Cement Hydrationxe2x80x9d, J. Am. Ceram. Soc., 68[1]:10-16; R. Blinc et al., xe2x80x9cNMR Relaxation Study of Adsorbed Water in Cement and Tricalcium Silicate Pastesxe2x80x9d, J. Am. Ceram. Soc., 61[1]:35-39; and L. Barbic et al., xe2x80x9cThe Determination of Surface Development in Cement Pastes by NMRxe2x80x9d, J. Am. Ceram. Soc., 65[1]:25-30.
Thus, although using T1 measurements to determine properties of concrete while hardening is well known, using spin-echo methods for making T2 measurements have not been successful. As mentioned above, one of the main reasons for the lack of success in making T2 measurements is the short relaxation times. However, the very same short T2 relaxation times make it desirable to develop a method which uses T2 measurements instead of T1, because the concrete property information is obtained much quicker. The present invention provides such methods.
A method of using T2 measurements for determining concrete strength, potential shrinkage, and readiness to accept coverings on concrete samples in situ is described in U.S. Pat. No. 5,672,968.
Column 1, lines 20-24 of U.S. Pat. No. 5,672,968 (hereinafter ""968), recites:
The water in concrete appears in three states during curingxe2x80x94chemically bound, capillary bound, and free water. The relative fraction of water in these three states changes during curing with some of the water evaporating away from the concrete surface.
It will be appreciated in this respect that there are no xe2x80x9cfree waterxe2x80x9d in the structure of cement and concrete mixture (right after the beginning of hardening), and certainly not in the structure of the hardened concrete. According to the fundamental definitions of the theory of drying of capillary-porous bodies, free water is the water capable of moving under the influence of gravity forces. Such behavior of we ate is typical for capillaries, whose size is larger than 10xe2x88x923 cm. (see, A. V. Likov xe2x80x9cTheory of drying. Moscow, xe2x80x9cEnergijaxe2x80x9d, 1968, p. 472. According to T. C. Powers xe2x80x9cStructure and Physical Properties of Hardened Portland Cement Pastexe2x80x9d. J. Amer. Ceramic Soc., 41, pp. 1-6 (January 1958), the primary capillary porosity is determined by characteristic diameter of pores (2.5-5.0)xc3x9710xe2x88x924 cm, already at the stage of fresh-made concrete paste. This means that the water in the structure is found under the field of capillary forces from start, i.e., time zero, such that in effect there are no free water in concrete.
Furthermore, the relative water content in cement and concrete changes (decreases) primarily due to chemical bounding, and not as a result of water evaporation.
Column 1, lines 25-30 of ""968, recites:
It is known that the amount of water that ends up chemically bound is highly correlated to the compressive strength of the concrete.
It will be appreciated in this respect that there is no, and cannot be, any correlation between the amount of chemically bound water and the hardness of concrete under pressure, because, only the level of capillary-porosity structure development and its properties determine the hardness of concrete and of other similar materials, which porosity is highly correlated to physically bound water and is not at all correlated the chemically bound water.
Column 3, lines 55-60 of ""968 recites:
The present invention uses low frequency (approximately 1 MHz) NMR, which the inventors have found to provide the desired quality of spin-echo measurements.
This and similar recitations to the effect that the ""968 technology uses low frequency (approximately 1 MHz) NMR appear in numerous other locations along the specification of ""968, including, for example, on column 4, line 21, column 5, line 33 and column 7, line 2 and in the claims.
In all of these cases, the low-frequency (approximately 1 MHz) dimension of spin-echo NMR is claimed to be a distinguishing feature of the ""968 technology. However, low frequency of the magnetic field is a significant disadvantage. In the experiments described in ""968 (see FIGS. 2, 3 and 4 of ""968) it is seen that the minimal possible time of T2 relaxation, available for measuring, equals about 0.5 msec. Thus, more than 35% of water contained in the concrete structure remain xe2x80x9cinvisiblexe2x80x9d. These 35%, however, are the fraction of water which are most adhered to the porous matrix and reflect its properties to the highest extent. Therefore, all of the conclusions and statements derived from these experiments are highly arguable and practically indemonstrable.
Column 4, lines 1-7 of ""968 recites:
The water appears in the concrete in three different stages:
a. Free waterxe2x80x94T2 relaxation time of 50-200 ms.
b. Capillary bound waterxe2x80x94T2 relaxation time of 15-30 ms.
c. Chemically bound waterxe2x80x94T2 relaxation time less than 0.2 ms.
See to this effect also column 6, lines 49-55 of ""968. However, it is known that using T2 measurement the relaxation time of free water, which is at all absent from cement paste and/or concrete structures, is in the order of 3 seconds, that of physically bound water (both in cement gel pores and in larger capillaries) is in the range of 30-100 xcexcsec, and that of chemically bound water is in the range of 10-17 xcexcsec.
To this effect see Mendelson K. S., Halperin W. P., Jehng J-Y., Song Y-Q. xe2x80x9cSurface magnetic relaxation in cement pastesxe2x80x9d. Magnetic Resonance Imaging, Vol. 12., No. 2, pp. 207-208, 1994; Halperin W. P, Halperin W. P., Jehng J-Y., Song Y-Q. xe2x80x9cApplication of spin-spin relaxation time measurement of surface area and pore size distribution in a hydrating cement pastexe2x80x9d. Magnetic Resonance Imaging, Vol. 12, No. 2, pp. 169-173, 1994; Lahajnar G., Blinc R., Rutar V., Smoley V., Zupan cic 1., Kocuvan I., Ursic J. xe2x80x9cOn the use of pulse NMR techniques for the study of cement hydrationxe2x80x9d. Cement and Concrete Research, Vol. 7, pp. 385-394, 1977; Milykovic L., Lasis D., MacTavish J. C., Pintar M. M., Blinc R., Lahajnar G. xe2x80x9cNMR studies of hydrating cement: a spin-spin relaxation study of the early hydration stagesxe2x80x9d. Cement and Concrete Research, Vol. 18, pp. 951-956, 1988.
It is evident from FIGS. 2-4 of ""968 that all of the measurements therein were performed in the T2 time intervals from approximately 0.5 msec to 1,300 msec. From the described distribution of water energy levels it is totally unclear what states of liquids were actually measured and which levels of liquids bonding with solid phase correspond to the peaks at values T2=0.5-15 msec; T2=30-50 msec; and T2 greater than 200 msec. In other words, most of the measured T2 interval, i.e., below 0.5 msec, which reflects the more tightly bound water in fine pores and capillaries was not measured, nor was it analyzed.
Capillary (physically) bound water is determined by the authors of ""968 within an extremely narrow interval of T2 relaxation times, i.e., T2=15-30 msec. It is known that the porosity of cement stone and concrete changes in a very wide diapason from 15-100 xc3x85 (gel pores) up to 10xe2x88x924 cm. To this effect, see, T. C. Powers xe2x80x9cStructure and Physical Properties of Hardened Portland Cement Pastexe2x80x9d. J. Amer. Ceramic Soc., 41, pp. 1-6 (January 1958); and Neville A. M., xe2x80x9cProperties of concretexe2x80x9d 3-rd Edition. Longman Scientific and Technical, N-Y, 1988). There are experimental data of T2 values of physically bound water contained in various capillary-porous bodies as follows: fired-clay brickxe2x80x94T2=360-620 xcexcsec., sand-lime brickxe2x80x94T2=1,700 xcexcsec, mortarxe2x80x94T2=2000 xcexcsec. To this effect, see Pel L., Kopinga K., Bertram G., Lang G. xe2x80x9cWater absorption in fired-clay brick observed by NMR scanningxe2x80x9d. J. Phys. D.: Appl. Phys. Vol. 28, pp. 675-680, 1995; and Pel L., Kopinga K., Brocken H. xe2x80x9cWater transport in porous building materialsxe2x80x9d. HERON 41, pp. 95-105, 1996.
Thus the values T2=15-30 msec recited in ""968 for capillary bound water corresponds to water present in large capillaries with a characteristic size of 10xe2x88x924 cm. In turn, the whole broad spectrum of water states in capillary pores is left unmonitored or determined.
It is principally impossible to obtain a correlation between a particular, according to its quantity, concrete property, for example, strength, and spectrogram xe2x80x9camplitude of NMR-time relaxation T2xe2x80x9d (FIGS. 2 and 3 of ""968), which is only a graphic illustration of some measured distribution. Moreover, character and form of the spectrograms, measured for the concrete of the same content at the same time of its hardening by means of various NMR spectrographs can differ. considerably, depending on the technical parameters of devices applied, and also depending on the specifics of processing of the measured experimental values (exponent value, etc.).
It will be appreciated that determination and prediction of concrete properties by means of correctional dependencies is possible only by means of juxtaposition of values of the given concrete property with specific numeral parameter values, determined according to the results of NMR-measurements.
The fact that the measured water content constitutes only about 65% (see FIG. 4 of ""968) of the real content thereof directly results due to the insufficient resolving power of the device CoreSpec-1000 which was employed. This device, which was originally developed for handling geophysical problems (search for oil in the ground, etc.), does not allow to measure low relaxation times, T2 less than 300 msec, thus, about 35% of water remains xe2x80x9cinvisiblexe2x80x9d. Consequently, the CoreSpec-1000 device is completely inapplicable for analysis of finely-dispersed capillary-porous systems such as cement stone and concrete.
There is, thus, still a widely recognized need for, and it would be highly advantageous to have, an operable and improved apparatus and methods for measuring and predicting properties of capillary-porous chemically active materials while hardening, devoid of the limitations of the prior art.
According to one aspect of the present invention there is provided a method for measuring a strength of a capillary-porous chemically active material while hardening, the capillary-porous chemically active material including therein water which undergoes stage metamorphosis and including a physically bound water portion, the method comprising the steps of performing a high at least 7 MHz, preferably at least 10 MHz, typically, between 10 MHz and 20 MHz, frequency, spin-echo nuclear magnetic resonance measurement of at least the physically bound water portion; and correlating the high frequency, spin-echo nuclear magnetic resonance measurement with a predetermined relationship between the strength and the high frequency, spin-echo nuclear magnetic resonance measurement.
According to another aspect of the present invention there is provided a method for determining a strength of a capillary-porous chemically active material while hardening, the capillary-porous chemically active material including therein water which undergoes stage metamorphosis and including a portion of physically bound water, the method comprising the steps of performing a spin-echo nuclear magnetic resonance measurement of at least the physically bound water portion; and correlating the spin-echo nuclear magnetic resonance measurement with a predetermined relationship between energy values of the physically bound water and the spin-echo nuclear magnetic resonance measurement, thereby determining the strength of the capillary-porous chemically active material while hardening.
According to yet another aspect of the present invention there is provided a method for measuring a strength of a capillary-porous chemically active material while hardening, the capillary-porous chemically active material including therein water which undergoes stage metamorphosis and including a physically bound water portion, the method comprising the steps of performing high at least 7 MHz frequency, spin-echo nuclear magnetic resonance measurements of at least the physically bound water at least at setting start point and at setting finish point; and extrapolating the strength based on a predetermined relationship between the strength and the high frequency, spin-echo nuclear magnetic resonance measurements.
According to still another aspect of the present invention there is provided a method for determining a strength of a capillary-porous lo chemically active material while hardening, the capillary-porous chemically active material including therein water which undergoes stage metamorphosis and including a portion of physically bound water, the method comprising the steps of performing spin-echo nuclear magnetic resonance measurements of at least the physically bound water at least at setting start point and at setting finish point; and extrapolating the strength based on a predetermined relationship between the strength and the spin-echo nuclear magnetic resonance measurements.
According to an additional aspect of the present invention there is provided a method of measuring a strength of a structure made of concrete while hardening, the concrete including therein physically bound water and chemically bound water, the method comprising the steps of performing an in situ, high at least 7 MHz frequency, spin-echo nuclear magnetic resonance measurement of at least the physically bound water; and correlating the high frequency, spin-echo nuclear magnetic resonance measurement with a predetermined relationship between the strength and the high at least 7 MHz frequency, spin-echo nuclear magnetic resonance measurement.
According to yet an additional aspect of the present invention there is provided a method of determining a strength of a structure made of concrete, the concrete including therein physically bound water and chemically bound water, the method comprising the steps of performing an in situ spin-echo nuclear magnetic resonance measurement of at least the physically bound water; and correlating the spin-echo nuclear magnetic resonance measurement with a predetermined relationship between energy values of the physically bound water and the spin-echo nuclear magnetic resonance measurement, thereby determining the strength of the structure made of concrete while hardening.
According to still an additional aspect of the present invention there is provided a method of predicting a strength of a structure made of concrete while hardening, the concrete including therein physically bound water and chemically bound water, the method comprising the steps of performing an in situ, a high at least 7 MHz frequency, spin-echo nuclear magnetic resonance (NMR) measurement of at least the physically bound water; and extrapolating the strength based on a predetermined relationship between the strength and the high frequency, spin-echo nuclear magnetic resonance measurement.
According to a further aspect of the present invention there is provided a method of predicting a strength of a structure made of concrete while hardening, the concrete including therein physically bound water and chemically bound water, the method comprising the steps of performing an in situ spin-echo nuclear magnetic resonance (NMR) measurement of at least the physically bound water; and extrapolating the strength based on a predetermined relationship between the strength and the spin-echo nuclear magnetic resonance measurement, a radio frequency shield is employed to substantially isolate the spin-echo nuclear magnetic resonance measurement from environmental noise.
According to yet a further aspect of the present invention there is provided an apparatus for measuring a strength of a structure made of a capillary-porous chemically active material, the capillary-porous chemically active material having a surface and including therein physically bound water and chemically bound water, the apparatus comprising a pulsed nuclear magnetic resonance generator for generating a sensitive volume in the concrete structure for performing therein an in situ, high at least 7 MHz frequency, spin-echo nuclear magnetic resonance measurement of at least the physically bound water in the capillary-porous chemically active material while hardening, the pulsed nuclear magnetic resonance generator including in an operative arrangement (a) a static magnetic field generator for generating a static magnetic field within the sensitive volume, the static magnetic field generator including at least one magnet so designed such that static magnetic field lines of the static magnetic field are disposable close (e.g., 5-30 mm, preferably 15-20 mm) and substantially perpendicular to the surface; (b) a radio frequency electromagnetic field generator for generating a radio frequency electromagnetic field, the radio frequency electromagnetic field generator including at least one radio frequency coil so designed such that electromagnetic field lines of the radio frequency electromagnetic field are disposable substantially parallel to the surface; and (c) a nuclear magnetic resonance receiver for receiving nuclear magnetic resonance signals form excitable nuclei in the capillary-porous chemically active material and for providing an output indicative of a strength of the capillary-porous chemically active materials.
According to still a further aspect of the present invention there is provided an apparatus for measuring a strength of a structure made of a capillary-porous chemically active material, the capillary-porous chemically active material having a surface and including therein physically bound water and chemically bound water, the apparatus comprising a pulsed nuclear magnetic resonance generator for generating a sensitive volume in the concrete structure for performing therein an in situ, spin-echo nuclear magnetic resonance measurement of at least the physically bound water in the capillary-porous chemically active material while hardening, the pulsed nuclear magnetic resonance generator including in an operative arrangement (a) a static magnetic field generator for generating a static magnetic field within the sensitive volume, the static magnetic field generator including at least one magnet so designed such that static magnetic field lines of the static magnetic field are disposable close and substantially perpendicular to the surface; (b) a radio frequency electromagnetic field generator for generating a radio frequency electromagnetic field, the radio frequency electromagnetic field generator including at least one radio frequency coil so designed such that electromagnetic field lines of the radio frequency electromagnetic field are disposable substantially parallel to the surface; and (c) a nuclear magnetic resonance receiver for receiving nuclear magnetic resonance signals form excitable nuclei in the capillary-porous chemically active material and for providing an output indicative of a strength of the capillary-porous chemically active materials.
According to further features in preferred embodiments of the invention described below,.each of the at least one radio frequency-coil is shaped as a frustum having a smaller base and a wider top and is disposable with its longitudinal axis perpendicular to the surface and having its smaller base disposable on the surface.
According to still further features in the described preferred embodiments the at least one magnet includes a horseshoe magnet having its opening disposable against the surface.
According to still further features in the described preferred embodiments the at least one magnet includes one larger and one smaller horseshoe magnets.
According to still further features in the described preferred embodiments the at least one magnet has a butterfly-type cross section.
According to still further features in the described preferred embodiments the at least one magnet includes an upside-down xe2x80x9cTxe2x80x9d-bar magnet.
The present invention successfully addresses the shortcomings of the presently known configurations by providing an apparatus and method for measuring and predicting properties of capillary-porous chemically active materials while hardening.